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February 28, 2015, 00:46 
Wrong fluctuation of pressure in transient simulation

#1 
New Member
Cai Tao
Join Date: Oct 2014
Location: China shanghai
Posts: 7
Rep Power: 4 
Hi.
I come across a problem in a transient simulation. I use the LES model to simulation a sequare cylinder, and set some pressure monitoring points. The results of the pressure have a strange fluctuation, which is shown in the follow pictures. the file of controDict // ************************************************** *********************** //libs ( ); application pisoFoam; startFrom latestTime; startTime 0; stopAt endTime; //stopAt writeNow; endTime 5; deltaT 5.0e6; writeControl timeStep; writeInterval 1000; purgeWrite 0; writeFormat ascii; writePrecision 6; writeCompression off; timeFormat general; timePrecision 6; runTimeModifiable true; functions { probes { type probes; functionObjectLibs ("libsampling.so"); enabled true; outputControl timeStep; outputInterval 1; probeLocations ( ( 0.06 0.02 0.08 ) ( 0.005 0.0095 0.08 ) ( 0.005 0.0305 0.08 ) ( 0.015 0.0095 0.08 ) ( 0.015 0.0305 0.08 ) } // ************************************************** *********************** // the file of fvScheme // ************************************************** *********************** // ddtSchemes { default backward; } d2dt2Schemes { } gradSchemes { default Gauss linear; grad(nuTilda) cellLimited Gauss linear 1; grad(U) cellLimited Gauss linear 1; } divSchemes { default none; div(phi,U) Gauss LUST unlimitedGrad(U); //div(phi,U) Gauss linearUpwind unlimitedGrad(U); div(phi,k) Gauss limitedLinear 1; div(phi,nuTilda) Gauss limitedLinear 1; div((nuEff*dev(T(grad(U))))) Gauss linear; } laplacianSchemes { default Gauss linear limited corrected 0.33; } interpolationSchemes { default linear; } snGradSchemes { default limited corrected 0.33; } fluxRequired { default no; p; } // ************************************************** *********************** // the file of fvSolution // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * // solvers { p { solver GAMG; tolerance 1e6; relTol 0.1; smoother GaussSeidel; nPreSweeps 0; nPostSweeps 2; nFinestSweeps 40; cacheAgglomeration on; agglomerator faceAreaPair; nCellsInCoarsestLevel 128; mergeLevels 1; } pFinal { $p; tolerance 1e6; relTol 0; }; "(UkBnuTilda)" { solver smoothSolver; smoother GaussSeidel; tolerance 1e07; relTol 0.1; } "(UkBnuTilda)Final" { $U; tolerance 1e7; relTol 0; }; } PISO { nCorrectors 2; nNonOrthogonalCorrectors 5; pRefCell 0; pRefValue 0; } relaxationFactors { "U.*" 1; "p.*" 1; "nuTilda.*" 1; } // ************************************************** *********************** // part of the file of the log Time = 0.12566 Courant Number mean: 0.00839828 max: 0.310058 smoothSolver: Solving for Ux, Initial residual = 3.6145e05, Final residual = 1.33368e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.00041477, Final residual = 1.43826e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.00079561, Final residual = 3.29873e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00910454, Final residual = 0.000548275, No Iterations 1 GAMG: Solving for p, Initial residual = 0.002062, Final residual = 0.000200861, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00120839, Final residual = 9.88252e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000657611, Final residual = 6.04321e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000334683, Final residual = 2.98511e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000201084, Final residual = 1.9542e05, No Iterations 3 time step continuity errors : sum local = 1.57267e11, global = 3.70403e14, cumulative = 2.7449e12 GAMG: Solving for p, Initial residual = 0.00336111, Final residual = 0.00018496, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00165023, Final residual = 0.0001041, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000837023, Final residual = 6.35304e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000429824, Final residual = 4.20207e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000238282, Final residual = 2.09567e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144679, Final residual = 9.81141e07, No Iterations 80 time step continuity errors : sum local = 8.19777e13, global = 3.70403e14, cumulative = 2.70786e12 ExecutionTime = 6263.22 s ClockTime = 6361 s Time = 0.125665 Courant Number mean: 0.00839835 max: 0.310065 smoothSolver: Solving for Ux, Initial residual = 3.61455e05, Final residual = 1.33319e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414767, Final residual = 1.43823e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795566, Final residual = 3.29825e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00916193, Final residual = 0.0005405, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00205039, Final residual = 0.00019946, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00118592, Final residual = 9.89506e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000645054, Final residual = 6.05196e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000332466, Final residual = 3.01745e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000198621, Final residual = 1.98006e05, No Iterations 3 time step continuity errors : sum local = 1.59175e11, global = 6.0819e14, cumulative = 2.76868e12 GAMG: Solving for p, Initial residual = 0.00335465, Final residual = 0.000184149, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164526, Final residual = 0.000104069, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000834565, Final residual = 6.34114e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000428368, Final residual = 4.17622e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000237407, Final residual = 2.04899e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.00014399, Final residual = 9.93928e07, No Iterations 77 time step continuity errors : sum local = 8.52212e13, global = 6.0819e14, cumulative = 2.8295e12 ExecutionTime = 6310.82 s ClockTime = 6409 s Time = 0.12567 Courant Number mean: 0.00839843 max: 0.310072 smoothSolver: Solving for Ux, Initial residual = 3.61467e05, Final residual = 1.33373e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414775, Final residual = 1.43828e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795495, Final residual = 3.29769e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.0091657, Final residual = 0.00054717, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00205872, Final residual = 0.000199804, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00120643, Final residual = 9.84e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000656809, Final residual = 6.01974e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000334246, Final residual = 2.96852e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000200805, Final residual = 1.95013e05, No Iterations 3 time step continuity errors : sum local = 1.56932e11, global = 3.71509e14, cumulative = 2.79235e12 GAMG: Solving for p, Initial residual = 0.00336065, Final residual = 0.000184732, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164948, Final residual = 0.000103936, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000836544, Final residual = 6.33963e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000429508, Final residual = 4.19258e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00023813, Final residual = 2.08646e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.00014451, Final residual = 9.97118e07, No Iterations 79 time step continuity errors : sum local = 8.31101e13, global = 3.71509e14, cumulative = 2.75519e12 ExecutionTime = 6358.9 s ClockTime = 6457 s Time = 0.125675 Courant Number mean: 0.0083985 max: 0.310079 smoothSolver: Solving for Ux, Initial residual = 3.61467e05, Final residual = 1.33325e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414768, Final residual = 1.43821e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.00079544, Final residual = 3.29733e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00908316, Final residual = 0.000539338, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00204978, Final residual = 0.000199266, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00118581, Final residual = 9.87077e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000644816, Final residual = 6.03733e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000332293, Final residual = 3.01533e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000198653, Final residual = 1.98122e05, No Iterations 3 time step continuity errors : sum local = 1.59243e11, global = 6.10176e14, cumulative = 2.81621e12 GAMG: Solving for p, Initial residual = 0.00335482, Final residual = 0.000184184, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164542, Final residual = 0.000104145, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000834698, Final residual = 6.35111e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000428487, Final residual = 4.18969e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000237558, Final residual = 2.06722e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144187, Final residual = 9.92679e07, No Iterations 79 time step continuity errors : sum local = 8.51382e13, global = 6.10176e14, cumulative = 2.87723e12 ExecutionTime = 6407.22 s ClockTime = 6506 s Time = 0.12568 Courant Number mean: 0.00839857 max: 0.310086 smoothSolver: Solving for Ux, Initial residual = 3.61473e05, Final residual = 1.33375e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414769, Final residual = 1.43821e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795392, Final residual = 3.29701e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00903316, Final residual = 0.000545484, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00205756, Final residual = 0.000199936, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0012069, Final residual = 9.83739e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000657011, Final residual = 6.01633e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000334339, Final residual = 2.97385e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000200948, Final residual = 1.94727e05, No Iterations 3 time step continuity errors : sum local = 1.56695e11, global = 3.72636e14, cumulative = 2.83997e12 GAMG: Solving for p, Initial residual = 0.00336013, Final residual = 0.000184686, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164964, Final residual = 0.00010392, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000836632, Final residual = 6.34008e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000429559, Final residual = 4.19243e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000238137, Final residual = 2.08849e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144556, Final residual = 9.82253e07, No Iterations 79 time step continuity errors : sum local = 8.19351e13, global = 3.72636e14, cumulative = 2.8027e12 ExecutionTime = 6455.37 s ClockTime = 6554 s Time = 0.125685 Courant Number mean: 0.00839865 max: 0.310093 smoothSolver: Solving for Ux, Initial residual = 3.61477e05, Final residual = 1.33329e07, No Iterations 1 smoothSolver: Solving for Uy, Initial residual = 0.000414766, Final residual = 1.43816e06, No Iterations 1 smoothSolver: Solving for Uz, Initial residual = 0.000795332, Final residual = 3.29664e06, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00902425, Final residual = 0.000538001, No Iterations 1 GAMG: Solving for p, Initial residual = 0.00204822, Final residual = 0.000198808, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00118526, Final residual = 9.88807e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000645015, Final residual = 6.0607e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000332475, Final residual = 3.02826e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000198705, Final residual = 1.66574e05, No Iterations 4 time step continuity errors : sum local = 1.34104e11, global = 6.12341e14, cumulative = 2.86394e12 GAMG: Solving for p, Initial residual = 0.0033574, Final residual = 0.00018402, No Iterations 2 GAMG: Solving for p, Initial residual = 0.00164436, Final residual = 0.000103905, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000834272, Final residual = 6.33415e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000428371, Final residual = 4.17247e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000237515, Final residual = 2.0474e05, No Iterations 3 GAMG: Solving for p, Initial residual = 0.000144517, Final residual = 9.88653e07, No Iterations 77 time step continuity errors : sum local = 8.48563e13, global = 6.12341e14, cumulative = 2.92517e12 ExecutionTime = 6500.77 s ClockTime = 6601 s actually， I have once slove this problem by change the mesh, see the post "A shock appears after several periods of the transient simulation"http://www.cfdonline.com/Forums/openfoamsolving/143751shock appearsafterseveralperiodstransientsimulation.html. but now, this method seems useless. Can someone come across such problem. maybe we can have a disscussion. 

February 28, 2015, 09:33 

#2 
Senior Member
anonymous
Join Date: Aug 2014
Posts: 204
Rep Power: 6 
Maybe you should let te simulation run for a lot more of time. I don't think that it has had enough time to settle.
If you've already tried it, we could dip in it further 

March 5, 2015, 22:33 

#3  
New Member
Cai Tao
Join Date: Oct 2014
Location: China shanghai
Posts: 7
Rep Power: 4 
Quote:
I have run this case form time 0.125s to 0.24s, and the result is still unsatisfactory. The attached pictures are the result. Do you think I need to keep runing this case? or maybe I need to change some sets? 

Tags 
pressure, transient simulation, wrong fluctuation 
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